Embryology of branchial arches applied anatomy by osama elhamzawy

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Health & Medicine

Published on December 2, 2013

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Embryology of Branchial Arches (Applied Anatomy)

Embryology of Branchial Arches & Nerve Supply ((Applied Anatomy By: Osama Elhamzawy Faculty of Medicine Alexandria University - Egypt

Introduction: During the pre –Embryonic period, the cells differentiate into three germ layers: Ectoderm (outside layer( Mesoderm (middle layer( Endoderm (inside layer(

Introduction:  Ectoderm gives rise to the CNS, peripheral nervous system; sensory epithelia of the eye, ear, and nose; epidermis and its appendages (hair and nails(.  Neural crest cells derived from neuroectoderm, give rise to the cells of the spinal, cranial (cranial nerves V, VII, IX, and X(, and autonomic ganglia; ensheathing cells of the peripheral nervous system; pigment cells of the dermis; muscle, connective tissues, and bone of pharyngeal arch origin and meninges (coverings( of the brain and spinal cord.

Introduction:  Mesoderm gives rise to connective tissue; cartilage; bone; striated and smooth muscles; blood, and lymphatic vessels; heart, kidneys; ovaries; testes; genital ducts; serous membranes lining the body cavities (pericardial, pleural, and peritoneal(; spleen; and cortex of suprarenal glands.  Endoderm gives rise to the epithelial lining of the gastrointestinal and respiratory tracts, urinary bladder , tympanic cavity, tympanic antrum, and auditory tube parenchyma of the tonsils, thyroid and parathyroid glands, thymus, liver, and pancreas.

Pharyngeal arches begin to develop Arches  The pharyngeal early in the fourth week as neural crest cells migrate into the future head and neck regions.  The first pair of pharyngeal arches, the primordium of the jaws, appears as surface elevations lateral to the developing pharynx.  Soon other arches appear as obliquely disposed, rounded ridges on each side of the future head and neck regions.

Pharyngeal Arches fourth week, four  By the end of the arches are visible externally. pairs of pharyngeal  The fifth and sixth arches are rudimentary and are not visible on the surface of the embryo.  The pharyngeal arches are separated from each other by the pharyngeal grooves. Like the pharyngeal arches, the grooves are numbered in a craniocaudal sequence.

Pharyngeal Apparatus Pharyngeal apparatus consists of:  Pharyngeal arches  Pharyngeal pouches  Pharyngeal grooves  Pharyngeal membrane

Pharyngeal Arch Components  Each pharyngeal arch consists of a core of mesenchyme  Is covered externally by ectoderm and internally by endoderm  In the third week the original mesenchyme is derived from mesoderm  But during the fourth week most of the mesenchyme is derived from neural crest cells that migrate into the pharyngeal arches

Fate of Pharyngeal Arches  During the fifth week, the second pharyngeal arch enlarges and overgrows the third and fourth arches, forming the ectodermal depression called cervical sinus  By the end of seventh week the second to fourth pharyngeal grooves and the cervical sinus have disappeared, giving the neck a smooth contour

Fate of Pharyngeal Arches A typical pharyngeal arch contains:  An aortic arch, an artery that arises from the truncus arteriosus of the primordial heart  A cartilaginous rod that forms the skeleton of the arch  A muscular component that differentiates into muscles in the head and neck  A nerve that supplies the mucosa and muscles derived from the arch

First Pharyngeal Arch cartilage  The dorsal end (Meckel cartilage) ossifies to form malleus and incus  The middle part forms anterior ligament of malleus (sphenomandibular ligament)  Ventral part forms primordium of the mandible  The cartilage disappears as mandible develops around it

Second Pharyngeal Arch cartilage  The dorsal end (Reichert cartilage) ossifies to form the stapes and styloid process of the temporal bone  The ventral end ossifies to form the lesser cornu and superior part of the body of the hyoid bone  Its perichondrium forms the stylohyoid ligament

Third, Fourth, Fifth and Sixth Pharyngeal Arches cartilages  The third arch cartilage ossifies to form the greater cornu and the inferior part of the body of the hyoid bone  The fourth and sixth arch cartilages fuse to form the laryngeal cartilages except epiglottis which develops from hypopharyngeal eminence  The fifth pharyngeal arch is rudimentary and has no derivatives

Derivatives of Pharyngeal Arch Muscles  The musculature of the first pharyngeal arch forms the muscles of mastication  The second pharyngeal arch forms the stapedius, stylohyoid, posterior belly of digastric, auricular and muscles of facial expression  The third arch forms the stylopharyngeus  The fourth arch forms cricothyroid and constrictors of pharynx  Sixth pharyngeal arch forms the intrinsic muscles of the larynx

Derivatives of Pharyngeal Arch Nerves       The first pharyngeal arch supplied by the caudal two branches of Trigeminal nerve (maxillary and mandibular) The second pharyngeal arch supplied by facial nerves supply, and caudal (fourth to sixth) arches respectively The third pharyngeal arch supplied by glossopharyngeal nerve Fourth to sixth supplied by vagus The fourth arch is supplied by superior laryngeal branch of vagus nerve The sixth arch is supplied by its recurrent laryngeal branch

Pharyngeal Pouches  There are four well defined pairs of pharyngeal pouches  The pairs of pouches develop in a craniocaudal sequence between the arches  The fifth pair is absent or rudimentary

Pharyngeal Pouches  The endoderm of the pouches contacts the ectoderm of the pharyngeal grooves and together they form the double layered pharyngeal membranes that separate the pharyngeal pouches from the pharyngeal grooves

First Pharyngeal Pouch  The first pharyngeal pouch expands into an elongate tubotympanic recess  And forms the endoderm lines the future Eustachian tube , middle ear, mastoid antrum.  And inner layer of the tympanic membrane

Second Pharyngeal Pouch  The second pharyngeal pouch is largely obliterated as the palatine tonsils develop  Part of the cavity of this pouch remains as the tonsillar sinus or fossa  The endoderm of the pouch proliferates and grows into the underlying mesenchyme  The central parts of these buds form crypts

Second Pharyngeal Pouch  The pouch endoderm forms the surface epithelium and the lining of the tonsillar crypts  At about 20 weeks the mesenchyme around the crypts differentiates into lymphoid tissue  These tissues soon organizes into the lymphatic nodules of the palatine tonsil

Third Pharyngeal Pouch  The third pharyngeal pouch expands and develops a solid, dorsal bulbar part and a hollow elongate ventral part  Its connection with the pharynx is reduced to a narrow duct that soon degenerates  By the sixth week the epithelium of each dorsal bulbar part begins to differentiate into inferior parathyroid gland

Third Pharyngeal Pouch  The epithelium of the elongate ventral parts of third pharyngeal pouch (primordia of thymus) proliferates and their cavities obliterate  These bilateral primordia of thymus come together in the median plane to form thymus  It descends into the superior mediastenum  The bilobed form of thymus remains throughout life  Each lobe has its capsule own blood supply, lymphatic drainage and nerve supply

Third Pharyngeal Pouch  The primordia of thymus and parathyroid glands lose their connections with the pharynx and migrate into the neck  Later the parathyroid glands separate from the thymus and lie on the dorsal surface of the thyroid gland

Fourth Pharyngeal Pouch  The fourth pharyngeal pouch also expands into dorsal bulbar and elongate ventral parts  Its connection with the pharynx is reduced to a narrow duct that soon degenerates  By the sixth week, each dorsal part develops into a superior parathyroid gland  It lies on the dorsal surface of the thyroid gland

Fourth Pharyngeal Pouch  The parathyroid glands derived from the third pouches descend with the thymus and are carried to a more inferior position than the parathyroid derived from the fourth pouches  This explains why the parathyroid glands derived from the third pair of pouches are located inferior to those from the fourth pouches

The Fifth Pharyngeal Pouch  When this develops, this rudimentary pouch becomes part of the fourth pharyngeal pouch and helps to form the ultimopharyngeal body that gives the calcitonin producing cells (parafollicular cells or C cells of the thyroid gland)

Pharyngeal Grooves  Only first pair persists as the external acoustic meatus  The other grooves normally obliterated with the cervical sinus as the neck develops

Pharyngeal Membranes  These membranes form where the epithelia of the grooves and pouches approach each other  Only first pharyngeal membrane becomes the tympanic membrane, others obliterate

Birth Defects Involving the Pharyngeal Region

Birth Defects Involving the Pharyngeal Region 1. Ectopic Thymic and Parathyroid Tissue 2. Branchial Fistulas 3. Neural Crest Cells and Craniofacial Defects • Treacher Collins syndrome (mandibulofacial dysostosis) • Robin sequence • DiGeorge anomaly • Velocardiofacial syndrome (VCFS) and conotruncal anomalies face syndrome • Oculoauriculovertebral spectrum (Goldenhar syndrome) 4. Thyroglossal Duct and Thyroid Abnormalities 5. Face anomalies 6. Palate anomalies

Birth Defects Involving the Pharyngeal Region 1. Ectopic Thymic and Parathyroid Tissue: Since glandular tissue derived from the pouches undergoes migration ; accessory glands or remnants of tissue may persist along the pathway particularly for thymic tissue, which may remain in the neck, and for the parathyroid glands. The inferior parathyroids are more variable in position than the superior ones and are sometimes found at the bifurcation of the common carotid artery.

Birth Defects Involving the Pharyngeal Region 2. Branchial Fistulas • • • • When the second pharyngeal arch fails to grow caudally over the third and fourth arches, leaving remnants of the second, third, and fourth clefts in contact with the surface by a narrow canal. These cysts are always on the lateral side of the neck in front of the sternocleidomastoid muscle. They commonly lie under the angle of the mandible and do not enlarge until later in life. Internal branchial fistulas are rare and occur when the cervical sinus is connected to the lumen of the pharynx by a small canal, which usually opens in the tonsillar region.

Birth Defects Involving the Pharyngeal Region 3. Neural Crest Cells and Craniofacial Defects Crest cells also contribute to the conotruncal endocardial cushions which septate the outflow tract of the heart into pulmonary and aortic channels So many infants with craniofacial defects may also have cardiac abnormalities such as: •Persistent truncus arteriosus •Tetralogy of Fallot •Transposition of the great vessels

Birth Defects Involving the Pharyngeal Region Examples of craniofacial defects involving crest cells: 1. Treacher Collins syndrome (mandibulofacial dysostosis) inherited as an autosomal dominant trait 60% of cases arising as new mutations Characterizaed by : •Malar hypoplasia due to underdevelopment of the zygomatic bones •Mandibular hypoplasia •Down-slanting palpebral fissures •Lower eyelid colobomas •Malformed external ears

Birth Defects Involving the Pharyngeal Region 2. DiGeorge anomaly: Characterizaed by: •Microstomia •Partial or complete absence of the thymus •immunological deficiencies •Hypocalcemia Prognosis: Poor

Birth Defects Involving the Pharyngeal Region 3. Oculoauriculovertebral spectrum (Goldenhar syndrome) Characterized by: •Number of craniofacial abnormalities that usually involve the maxillary, temporal, and zygomatic bones, which are small and flat. •Ear (anotia, microtia) •Eye (tumors and dermoids in the eyeball) •Vertebral (fused hemivertebrae spina bifida) •Cardiac abnormalities (Tetralogy of Fallot and ventricular septal defects)

Birth Defects Involving the Pharyngeal Region 4. Thyroglossal Duct and Thyroid Abnormalities lie at any point along the migratory pathway of the thyroid gland but is always near or in the midline of the neck Thyroglossal fistula Usually arises secondarily after rupture of a cyst but may be present at birth.

Birth Defects Involving the Pharyngeal Region 5- Face anomalies

Birth Defects Involving the Pharyngeal Region 5- Face anomalies

Birth Defects Involving the Pharyngeal Region 5- Face anomalies 1-cleft upper lip: •May be uni/bilateral •There is a defect between the philtrum and the lateral part of the lip •It is due to failure of fusion between the maxillary process and intermaxillary process •Common in males 2-oblique facial cleft: •It is a defect in the face from the medial angle of the eye crossing the side of the nose to the upper lip •It is due to failure of fusion between Maxillary process and the lateral and medial nasal processes •Nasolacrimal duct is exposed to ant. 3-median cleft lower lip: •It is due to failure of fusion between the mandibular processes (rare)

Birth Defects Involving the Pharyngeal Region 5- Face anomalies 4-macrostomia: It is due to arrest of fusion between Maxillary and mandibular processes to shift the angles medially 5-microstomia: It is due to excessive fusion bet. The maxillary and mandibular processes

Birth Defects Involving the Pharyngeal Region 5- Face anomalies

Birth Defects Involving the Pharyngeal Region 5- Face anomalies

Birth Defects Involving the Pharyngeal Region 6- Palate anomalies 1-cleft palate: Fomes: •Bifid uvula •Cleft soft palate •Cleft hard palate and soft palate It is due to failure of fusion between the two palatine processes posterior or with the primary palate anterior 2-perforated palate: •It is due to failure of fusion between The 2 palatine processes at certain point at midline.

Birth Defects Involving the Pharyngeal Region 6- Palate anomalies

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